Wastewater New York State Practice Exam

A properly designed primary clarifier is expected to remove what percentage of settleable solids?

1. 50 percent

2. 70 percent

3. 90 percent

4. 95 percent

The correct answer is: 90 percent

A properly designed primary clarifier is typically expected to remove about 90 percent of settleable solids from wastewater. The primary clarifier operates by allowing heavier solids to settle to the bottom of the tank through gravity, while lighter materials and other non-settling solids are carried over to the next stages of treatment. The design and operational effectiveness of primary clarifiers depend on factors such as tank size, residence time, and flow rates. When functioning properly, these systems can efficiently separate the bulk of the solid materials from the influent wastewater, leading to substantial reductions in the organic load entering subsequent treatment processes. Achieving a 90 percent removal rate is significant as it plays a crucial role in minimizing the burden on secondary treatment processes, which typically handle dissolved and suspended organic materials not removed in the primary phase. This high percentage also underscores the importance of maintaining the clarifier’s performance to ensure compliance with regulatory requirements and overall system efficiency.